#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <assert.h>

char* my_strcat(char* dest, const char* src) {
	assert(dest && src);
	char* ret = dest;
	while (*dest) {
		dest++;
	}
	while (*dest++ = *src++);
	return ret;
}

int main() {
	char arr1[20] = "hello ";
	my_strcat(arr1, "world!");
	printf("%s\n", arr1);
	return 0;
}